1. Field of the Invention
The present invention relates to a storage system which stores data to be used by a computer in a computer system. More specifically, the present invention relates to a control method of a first storage system which can connect a host to one or more second storage systems and virtualize a device in the second storage system as its own device.
2. Description of the Related Art
With rapid progresses of information systems, such as easing of regulations of electronic storages, expansion of Internet businesses, documentation in electronic form of procedures, or the like, a rapid increase in the amount of data is drastically exhibited. In addition to such a rapid increase in the amount of data, demands by customers for long-term storage of business activity histories (business information, mail or the like) of an enterprise through a data backup to a disk device (Disk-to-Disk Backup) or a countermeasure against an inspection are increasing, and thus data to be stored in a storage system continues increasing rapidly. Accordingly, in an enterprise information system, a storage system of each division or each system is increased and the management of a complicated IT infrastructure is simplified or made efficient. In particular, expectations for simplification of the management of a storage device and the optimization of total cost by utilizing an optimum storage system according to the value of data are increasing.
As a method of reducing the management cost of a large-scale storage system, a storage virtualization technique as disclosed in Japanese Patent Laid-Open Publication No. 2005-11277 (Patent Document 1) is exemplified. Patent Document 1 discloses a storage virtualization technique (hereinafter, referred to as an external storage connection method) in which a first storage system is connected to one or more second storage systems and a device (hereinafter, referred to as a logical device) connected to a higher-level device such as a host or the like by the second storage system is provided to the host as a logical device of the first storage system therethrough. When receiving a request for input/output to a logical device from the host, the first storage system judges whether a device to be accessed corresponds to either a logical device of the second storage system or a physical device such as a disk device in the first storage system and allocates the request for input/output to a proper access destination according to the result of judgment.
By using the storage system having the external storage connection method disclosed in Patent Document 1, a storage system in which a plurality of storage systems having different attributes such as performance, reliability, cost, or the like are unified can be constructed. For example, by connecting an expensive, high-performance, high-reliability first storage system having an external storage connection method to a plurality of inexpensive, low-performance, low-reliability second storage systems, a tiered storage system capable of optimum data arrangement according to freshness or value of data can be implemented. By using such a tiered storage system, for the purpose of coping with the inspection, a large amount of information such as business information, mail, or the like on daily business activities can be stored for a long period at optimum cost according to the value of the respective information.
However, when the large amount of data is stored for a long period, as described above, it is important to keep and operate a large-scale storage device for storing the large amount of data at lower cost. For example, a large amount of power is consumed so as to drive the large-scale storage device, and thus power consumption needs to be reduced. Further, a storage period of data ranging from several years to tens years may exceed a life span of a storage device, thus the replacement of the storage device is indispensable during the long-term storage. Accordingly, in order to reduce the cost for data storage, it is preferable that the life span of the storage device is extended as long as possible and that the number of replacement times of the storage device is reduced.
On the other hand, most of data stored for a long period as described above is an archive such as business transaction information or mail. This type of data is most unlikely to be used in daily businesses.